The issue about adding multipath device's targets into qemu-pr-helper's namespace

Hi all, I have a namespace question about passthrough disk(multipath device). In case of enabling namespace and cgroups in qemu.conf, The target(s) of the multipath device won't be added into qemu-pr-helper's namespace under certain situation, It causes the PERSISTENT RESERVE command failure in guest. While user starts a vm, To build namespace, The qemuDomainSetupDisk() will be invoked via threadA(this thread id will be the qemu's pid), To build cgroup, The qemuSetupImagePathCgroup() will be invoked via threadB. Both of the functions invoke the virDevMapperGetTargets() trying to parse a multipath device to target paths string, Then fill the targetPaths[]. The issue I experienced is: After libvirtd started, Everything works well for the first booted vm which has the passthrough multipath device. But If I shut it down & start it again, OR keep it running & start another vm which has other passthrough multipath device, Then the target(s) of the fresh started vm won't be added into the related qemu-pr-helper's namespace and it causes PERSISTENT RESERVE command failure in the corresponding guest. I digged into code, In this situation, The targetPaths[] in qemuDomainSetupDisk() won't be filled, it keeps NULL after virDevMapperGetTargets() returns. The virDevMapperGetTargets doesn't fill targetPaths[] because the dm_task_run() of libdevmapper returns 0 with errno 9(Bad file descriptor). So far, I don't understand why the dm_task_run() return 0 in this situation. BTW, The virDevMapperGetTargets() can always successfully fill the targetPaths[] in qemuSetupImagePathCgroup(). Please refer to the following 2 tests: The multipath configuration on host: host:~ # multipath -l vm1-data (3600140582d9024bc13f4b8db5ff12de0) dm-11 FreeNAS,lv68 size=6.0G features='0' hwhandler='1 alua' wp=rw `-+- policy='service-time 0' prio=0 status=active `- 2:0:0:2 sdd 8:48 active undef running vm2-data (36001405fc5f29ace3ec4fb8acd32aae5) dm-8 FreeNAS,lv46 size=4.0G features='0' hwhandler='1 alua' wp=rw `-+- policy='service-time 0' prio=0 status=active `- 2:0:0:1 sde 8:64 active undef running =================================================================== Test A: host:~ # systemctl restart libvirtd host:~ # virsh list Id Name State -------------------- host:~ # host:~ # virsh domblklist vm1 Target Source ------------------------------------------ vda /opt/vms/vm1/disk0.qcow2 sda /dev/mapper/vm1-data host:~ # host:~ # virsh start vm1 Domain vm1 started host:~ # virsh list Id Name State --------------------------- 1 vm1 running host:~ # nsenter -t $(pidof qemu-pr-helper) -a bash host:~ # ls -l /dev/sd* brw-rw---- 1 root disk 8, 48 Jul 14 16:30 /dev/sdd host:~ # exit exit host:~ # vm1:~ # lsscsi [0:0:0:0] disk FreeNAS lv68 0123 /dev/sda vm1:~ # vm1:~ # sg_persist --in -k /dev/sda FreeNAS lv68 0123 Peripheral device type: disk PR generation=0x0, there are NO registered reservation keys vm1:~ # host:~ # virsh shutdown vm1 Domain vm1 is being shutdown host:~ # virsh list Id Name State -------------------- host:~ # host:~ # virsh start vm1 Domain vm1 started host:~ # virsh list Id Name State --------------------------- 2 vm1 running host:~ # nsenter -t $(pidof qemu-pr-helper) -a bash host:~ # ls -l /dev/sd* ls: cannot access '/dev/sd*': No such file or directory host:~ # exit exit host:~ # vm1:~ # sg_persist --in -k /dev/sda FreeNAS lv68 0123 Peripheral device type: disk PR in (Read keys): Aborted command Aborted command vm1:~ # =================================================================== Test B: host:~ # systemctl restart libvirtd host:~ # virsh list Id Name State -------------------- host:~ # host:~ # virsh domblklist vm1 Target Source ------------------------------------------ vda /opt/vms/vm1/disk0.qcow2 sda /dev/mapper/vm1-data host:~ # host:~ # virsh start vm1 Domain vm1 started host:~ # virsh list Id Name State --------------------------- 1 vm1 running host:~ # nsenter -t $(pidof qemu-pr-helper) -a bash host:~ # ls -l /dev/sd* brw-rw---- 1 root disk 8, 48 Jul 14 17:28 /dev/sdd host:~ # exit exit host:~ # vm1:~ # lsscsi [2:0:0:0] disk FreeNAS lv68 0123 /dev/sda vm1:~ # vm1:~ # sg_persist --in -k /dev/sda FreeNAS lv68 0123 Peripheral device type: disk PR generation=0x0, there are NO registered reservation keys vm1:~ # host:~ # virsh list Id Name State --------------------------- 1 vm1 running host:~ # host:~ # virsh domblklist vm2 Target Source ------------------------------------------ vda /opt/vms/vm2/disk0.qcow2 sda /dev/mapper/vm2-data host:~ # host:~ # virsh start vm2 Domain vm2 started host:~ # virsh list Id Name State --------------------------- 1 vm1 running 2 vm2 running host:~ # nsenter -t $(qemu-pr-helper pid of vm2) -a bash host:~ # ls -l /dev/sd* ls: cannot access '/dev/sd*': No such file or directory host:~ # exit exit host:~ # vm2:~ # lsscsi [0:0:0:0] disk FreeNAS lv46 0123 /dev/sda vm2:~ # vm2:~ # sg_persist --in -k /dev/sda FreeNAS lv46 0123 Peripheral device type: disk PR in (Read keys): Aborted command Aborted command vm2:~ # =================================================================== Any comments will be much appreciated. Thanks in advance, Lin